Flexible stent

ABSTRACT

A flexible stent structure includes a plurality of axially spaced strut portions defining generally tubular axial segments of the stent and constructed to be radially expandable. A helical portion is interposed axially between two strut portions and has a plurality of helical elements connected between circumferentially spaced locations on the two strut portions. The helical elements extend helically between those locations and the length of a helical element is sufficient so that, when the stent is in a radially expanded state, it can simultaneously withstand repeated axial compression or expansion and bending.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 11/250,226 filed Oct. 14, 2005 which claims the benefit of U.S.Provisional Patent Application No. 60/667,613 filed Apr. 4, 2005 theentirety of both of which are hereby incorporated by reference into thisapplication.

BACKGROUND OF THE INVENTION

The present invention relates generally to expandable tubular structurescapable of insertion into small spaces in living bodies and, moreparticularly, concerns a stent structure which is capable of substantialand repeated flexing at points along its length without mechanicalfailures and with no substantial changes in its geometry.

A stent is a tubular structure that, in a radially compressed or crimpedstate, may be inserted into a confined space in a living body, such asan artery or other vessel. After insertion, the stent may be expandedradially to enlarge the space in which it is located. Stents aretypically characterized as balloon-expanding (BX) or self-expanding(SX). A balloon-expanding stent requires a balloon, which is usuallypart of a delivery system, to expand the stent from within and to dilatethe vessel. A self expanding stent is designed, through choice ofmaterial, geometry, or manufacturing techniques, to expand from thecrimped state to an expanded state once it is released into the intendedvessel. In certain situations higher forces than the expanding force ofthe self expanding stent are required to dilate a diseased vessel. Inthis case, a balloon or similar device might be employed to aid theexpansion of a self expanding stent.

Stents are typically used in the treatment of vascular and non-vasculardiseases. For instance, a crimped stent may be inserted into a cloggedartery and then expanded to restore blood flow in the artery. Prior torelease, the stent would typically be retained in its crimped statewithin a catheter and the like. Upon completion of the procedure, thestent is left inside the patient's artery in its expanded state. Thehealth, and sometimes the life, of the patient depend upon the stent'sability to remain in its expanded state.

Many available stents are flexible in their crimped state in order tofacilitate the delivery of the stent, for example within an artery. Feware flexible after being deployed and expanded. Yet, after deployment,in certain applications, a stent may be subjected to substantial flexingor bending, axial compressions and repeated displacements at pointsalong its length, for example, when stenting the superficial femoralartery. This can produce severe strain and fatigue, resulting in failureof the stent.

A similar problem exists with respect to stent-like structures. Anexample would be a stent-like structure used with other components in acatheter-based valve delivery system. Such a stent-like structure holdsa valve which is placed in a vessel.

SUMMARY OF THE INVENTION

In accordance with the present invention, a stent or a stent-likestructure is constructed to have different types of tubular portionsalong its length. In general, there are strut portions and helicalportions, where the strut portions are constructed primarily to provideradial expansion and radial strength, and the helical portions areconstructed primarily to permit repeated flexing and axial compressionand expansion. The flexing and axial compression are likely to berequired simultaneously, so the stent structure permits repeated andsubstantial flexing while in an axially compressed or expanded state,and it permits axial compression while in a flexed state. Preferably,strut portions are provided between helical portions or helical portionsare provided between strut portions. In a preferred embodiment, thestent is self-expanding and strut portions and helical portionsalternate along the length of the stent.

The stent is preferably constructed so that, in the expanded state thehelical portions permit axial compression or expansion of about 20%(preferably between 15% and 25%) and simultaneously permit bending witha minimum bending radius of about 13 mm (preferably between 10 mm and 16mm).

In accordance with another aspect of the invention, a helical portion ismade of helical elements which extend helically about the axis of thestent between points on two different strut portions which are spacedapart circumferentially by a distance which is more than approximately25% of the circumference of the stent (which is equivalent to an extentof 90 degrees about the axis of the stent) when it is in its expandedstate.

In accordance with yet another aspect of the invention, a helicalportion is made of helical elements which extend helically about theaxis of the stent between locations on two different strut portions. Inone embodiment a helical element is bi-directional, in that it extendsfirst in one circumferential direction and then the other between thetwo locations and has a peak.

In accordance with yet another aspect of the invention, a stent has aplurality of axially spaced strut portions defining generally tubularaxial segments of the stent and constructed to be radially expandable. Ahelical portion is interposed axially between two strut portions, andthe helical portion has a plurality of helical elements connectedbetween circumferentially spaced locations on two strut portions. Ahelical element extends helically between these locations, and at leastpart of the helical portion has a greater diameter than a strut portionwhen the stent is in an expanded state. In an alternate embodiment, atleast part of the helical portion has a smaller diameter than the strutportion when the strut is in an expanded state.

In one embodiment, the helical element is wound at least 90 degreesbetween strut elements connected to the helical element. In anotherembodiment, the helical element is wound at least 360 degrees betweenstrut elements connected to the helical element.

In an alternate embodiment, stent grafts are formed of a biocompatiblegraft material covering the outside, inside or both the outside andinside of the stent. The stent graft can have any embodiment of a stentstructure of the present invention. Stent graft devices are used, forexample, in the treatment of aneurysms, dissections andtracheo-bronchial strictures. The stent can also be coated with apolymer and/or drug eluting material as are known in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing description, as well as further objects, features, andadvantages of the present invention will be understood more completelyfrom the following detailed description of presently preferred, butnonetheless illustrative embodiments in accordance with the presentinvention, with reference being had to the accompanying drawings, inwhich:

FIG. 1A is a plan view of a first embodiment of a stent in accordancewith the present invention, the stent being shown in an unexpandedstate;

FIG. 1B is a plan view of the first embodiment of a stent in accordancewith the present invention, the stent being shown in a radially expandedstate;

FIG. 2 is a plan view of a second embodiment of a stent in accordancewith the present invention;

FIG. 3 is a plan view of a third embodiment of a stent in accordancewith the present invention;

FIG. 4 is a plan view of a fourth embodiment of a stent in accordancewith the present invention;

FIG. 5 is a sectional end view of a fifth embodiment of a stent inaccordance with the present invention;

FIG. 6 is a lengthwise side outline view of the same embodiment as FIG.5;

FIG. 7A is a plan view of another embodiment of a stent in accordancewith the present invention;

FIG. 7B is a plan view of another embodiment of the stent in accordancewith the present invention;

FIG. 8 is a sectional end view of another embodiment of the stent inaccordance with the present invention;

FIG. 9 is a lengthwise side outline view of the embodiment shown in FIG.8;

FIG. 10A is a sectional end view of an alternate embodiment of a stentin accordance with the present invention including graft materialcovering an outer surface of the stent;

FIG. 10B is a sectional end view of an alternate embodiment of a stentin accordance with the present invention including graft materialcovering an inner surface of the stent;

FIG. 10C is a sectional end view of an alternate embodiment of a stentin accordance with the present invention including graft materialcovering an outer surface and an inner surface of the stent;

FIG. 11A is a side view of an alternate embodiment of a stent inaccordance with the present invention including graft material attachedto the strut portion, the graft material covering the strut portion andthe helical portion;

FIG. 11B is a side view of an alternate embodiment of a stent inaccordance with the present invention including a plurality of sectionsof biocompatible graft material wherein a gap is provided between eachof the sections of graft material;

FIG. 11C is a side view of an alternate embodiment of a stent inaccordance with the present invention including a plurality of sectionsof a biocompatible graft material wherein the graft material of adjacentsections is overlapped;

FIG. 11D is a side view of an alternate embodiment of a stent inaccordance with the present invention including a biocompatible graftmaterial, the graft material having a bulge at the helical portions;

FIG. 11E is a side view of an alternate embodiment of a stent inaccordance with the present invention including a biocompatible graftmaterial, the graft material having a plurality of longitudinal openingsover the helical portions;

FIG. 11F is a side view of an alternate embodiment of a stent inaccordance with the present invention the graft material having a bulgeat the helical portions and the graft material having a plurality oflongitudinal openings over the helical portions;

FIG. 11G is a side view of an alternate embodiment of a stent inaccordance with the present invention including a biocompatible graftmaterial having a plurality of helical openings corresponding to a pitchof the helical elements;

FIG. 11H is a side view of an alternate embodiment of a stent inaccordance with the present invention including a plurality of sectionsof biocompatible graft material each of the sections being attached toeither the strut portion or the helical portion wherein a gap isprovided between each of the sections of graft material;

FIG. 11J is a side view of an alternate embodiment of a stent inaccordance with the present invention including a plurality of sectionsof biocompatible graft material, each of the sections being attached toeither the strut portion or the helical portion wherein adjacentsections of graft material is overlapped;

FIG. 12A is a plan view of an alternate embodiment of a stent in anexpanded state;

FIG. 12B is a plan view of the stent of FIG. 12A in a crimped state suchthat the gap between helical elements is the same throughout the helicalportions. Additionally, the length of the stent is the same in both thecrimped and expanded state;

FIG. 12C is a plan view of the stent of FIG. 12A in a crimped state suchthat the gap between helical elements changes throughout the helicalportion. Additionally, the stent is longer in the crimped state than theexpanded state; and

FIG. 13 is a plan view of an alternate embodiment of a stent inaccordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in greater detail to a preferred embodimentof the invention, an example of which is illustrated in the accompanyingdrawings. Wherever possible, the same reference numerals will be usedthroughout the drawings and the description to refer to the same or likeparts.

FIGS. 1A and 1B are plan views of a first embodiment of stent 10 inaccordance with the present invention shown in an unexpanded state andexpanded state, respectively. As used herein, the term “plan view” willbe understood to describe an unwrapped plan view. This could be thoughtof as slicing open a tubular stent along a line parallel to its axis andlaying it out flat. It should therefore be appreciated that, in theactual stent, the top edge of the FIG. 1A will be joined to the loweredge.

Stent 10 is made from a common material for self expanding stents, suchas Nitinol nickel-titanium alloy (Ni/Ti), as is well known in the art.Typically, the stent is laser cut from tubing, for example, with adiameter of about 5 mm (FIG. 1A). It is then expanded and set to adiameter of about 8 mm (FIG. 1B), and for pre-deployment it would becrimped to a diameter appropriate for the application, for example about3 mm. However, it is contemplated that the present invention isapplicable to any type and size of stent.

Stent 10 is generally made up of strut portion 12 and helical portion 14with axially aligned strut portion 12 alternating with helical portion14. In a preferred embodiment, strut portion 12 is positioned at eitherend of stent 10. Strut portion 12 being radially expandable upondeployment. Each strut portion 12 includes strut ring 16 having apattern of wave-like strut elements 16 a that progressescircumferentially about the stent. Each strut element 16 a has a widthequal to the peak to peak distance around the stent and a length equalto the peak-to-peak distance along the length of the stent. It will beappreciated that strut ring 16 could be partially straightened(stretched vertically in FIG. 1B) so as to widen strut elements 16 a andreduce their length. This is equivalent to expanding stent 10 radially.Preferably, the material of which stent 10 is made is such that strutelement 16 a will retain some wave-like shape in a radially expandedstate. For delivery, the stent would be crimped and fitted into acatheter, and it would expand after the catheter is inserted into thevessel and the stent is advanced out of the catheter.

Each helical portion is made up of a plurality of side-by-side helicalelements 18, each of which is helically wound about an axis of stent 10.Helical portion 14 is expandable radially upon deployment andcompressible, expandable and bendable in a deployed state. Helicalelements 18 can be connected between opposed individual wave portions ofstrut element 16 a of different strut portions 12. In this embodiment,each helical element 18 makes a complete rotation about the surface ofstent 10. However, they can make a partial rotation or more than onerotation. The helical portion is preferably constructed to permitrepeated axial compression or expansion of about 20% (preferably between15% and 25%) and simultaneously permit bending with a minimum bendingradius of about 13 mm (preferably between 10 mm and 16 mm), all withoutfailure.

Improved flexibility and axial compression can generally be accomplishedif helical element 18 is wound at least 90 degrees between strutelements 16 a connected to helical elements 18. Alternatively, helicalelement 18 is wound at least 360 degrees between strut elements 16 aconnected to helical elements 18.

FIG. 2 is a plan view of a second embodiment of stent 20 similar tostent 10 of FIG. 1. The primary differences are in the structure ofstrut portions 12′ and that there are right-handed and left-handedhelical portions (14R and 14L, respectively). Each strut portion 12′comprises two adjacent strut rings 26, 27 connected by short link 28.The closely opposed peaks of strut elements 26 a, 27 a are connected byshort link 28, so that each strut portion 12′ has a double strut ringstructure. It would also be possible to connect multiple strut ringstogether to form a larger strut portion. The advantage of twin ormultiple strut ring strut portions is that they offer increased radialstiffness over the single strut ring strut portion and can stabilize thestrut portions so they are less affected by axial forces.

In a right-handed helical portion 14R, the elements 18 progressclockwise about the surface of stent 10 and, in a left-handed helicalportion 14L, they progress counterclockwise. Helical elements 18essentially float and permit relatively large displacements about andalong the stent axis between the two strut ring portions at either end.In this embodiment, it will be appreciated that the diameter of thestent at each helical portion 14R, 14L is the same as the diameter ofthe stent at the strut portions 12 on either side. However, this neednot be the case, as will become evident from additional embodimentsdiscussed below. A benefit of using left-handed and right-handed helicalportions is that when the stent deploys the two portions rotate inopposite directions, maintaining the relative rotational positions ofdifferent axial portions of the stent.

FIG. 3 is another embodiment of stent 30 in accordance with the presentinvention. It is similar to stent 20 of FIG. 2, except that helicalportions 34 include helical element 38 which progresses bi-directionally(first counterclockwise and then clockwise) about the perimeter of stent30 between connection locations on two different strut portions 12′.Helical element 38 is wound at least 90 degrees from a first strutportion 12′ to peak 35 and is wound 90 degrees from peak 35 to a secondstrut portion 12′ in order to maintain flexibility. The one-directionalhelical elements 18 of FIG. 1A and 1B can allow adjacent strut portionsto rotate relative to one another. The bi-directional helical elements38 limit the amount adjacent strut portions can rotate about the stentaxis relative to one another but still provide axial and bendingflexibility.

FIG. 4 is a plan view of a fourth embodiment of a stent in accordancewith the present invention. In this case, stent 40 has strut portions12′ of FIG. 2 and the helical portions 14L, 14R (FIG. 2) and helicalportions 34 (FIG. 3). The advantage of this construction is thatcombining different types of helical elements allows a mix of propertiesas described herein, providing the opportunity for further optimizationof overall stent performance for a given application.

FIG. 5 is a sectional view perpendicular to the axis of a fifthembodiment of stent 30′ in accordance with the present invention, andFIG. 6 is a side outline view of the same embodiment. The stent has thestructure shown in FIG. 3, except that helical portions 38′ have alarger diameter than strut portions 12′. In this construction the radialstiffness of the helical portions is increased, but to a lesser degreethan the strut portions.

When all portions of the stent have the same diameter, the helicalportions may not have as much outward force on a vessel as the strutportions when the strut is expanded. The geometry of FIG. 6 will tend toforce the helical portions to expand more than the strut portions,increasing the outward force of the helical portions, which equalizesthe radial stiffness.

Nitinol structures have a biased stiffness, such that the force requiredto collapse the structure back towards the collapsed state is generallygreater than the force that continues to dilate the diseased vessel whenthe stent is in its expanded state. With some self expanding Nitinolstents, a balloon is used to assist the expansion/dilation of thevessel. The biased stiffness is enough to support the open vessel, butthe outward force may not be enough to open the vessel (or it may take alonger period of time). A stent with the type of geometry shown in FIG.5 would therefore be a good expedient to use in conjunction with balloonassisted expansion, or other applications requiring additional expansiveforce.

FIG. 7A is a plan view of another embodiment of stent 40B′ in accordancewith the present invention. Stent 40B′ includes strut member 42. Strutmember 42 progresses helically from one end of stent 40B′ to the other.Strut member 42 forms main body of stent 40B′. In this embodiment, eachstrut element 44 a is connected to a strut in a subsequent winding ofstrut member 42 by helical element 46. In this embodiment, helicalelement 46 of helical portion 45 progresses helically less than one fullrotation of 360 degrees about stent 40B′. Helical element 46 progressesin a direction opposite of the direction of which strut member 42progresses helically about stent 40B′.

Preferably, helical elements 46 are axially abutted, forming a type ofspring which permits a great deal of flexibility and axial expansion,while strut member 42 provides radial strength and retains the stent inits expanded condition.

FIG. 7B is a plan view of another embodiment of stent 40C′ in accordancewith the present invention. Stent 40C′ is similar to stent 40B′ andincludes strut member 42. Strut member 42 progresses helically from oneend of stent 40C′ to the other. Strut member 42 forms main body of stent40C′. In the present embodiment, each strut element 44 a is connected toa strut in a subsequent winding of strut member 42 by helical element47. In this embodiment, helical element 47 progresses helically aboutstent 40C′ in the same direction as strut member 42 progresses helicallyabout stent 40C′. Stent 40C′ includes transitional helical portions 49and strut portions 48 at either end of stent 40C′ to allow strut portion48 to be provided at either end of stent 40C′.

Stents 40B′ and 40C′ have the advantage that the flexible helicalelements are distributed more continuously along the length of the stentand may provide more continuous flexibility.

Those skilled in the art will appreciate that various modifications tostent 40B′ or 40C′ are possible, depending upon the requirements of aparticular design. For example, it might be desirable to connect fewerthan all of strut elements 44 a in a particular winding to a subsequentwinding, reducing the number of helical elements 46. Helical elements 46can extend for less or for any integer or non-integer multiple of arotation. A stent could also be made of a plurality of tubular sectionseach having the construction of stent 40B′ or 40C′ and joined lengthwiseby another type of section.

FIG. 8 is a sectional view perpendicular to the axis of an embodiment ofstent 20′ in accordance with the present invention, and FIG. 9 is a sideoutline view of the same embodiment. The stent has the structure shownin FIG. 1A, except that helical portions 14′ neck down to a smallerdiameter than strut portions 12′. In this construction the helicalportions will exert less force on the vessel wall than if the helicalportions were the same diameter. Reducing the force the stent exerts ona vessel wall can reduce the amount of damage done to a vessel andprovide a better performing stent.

FIGS. 10A-10C are sectional views perpendicular to the axis of the stentin accordance with the present invention. Stent graft 60, 70 and 80 havea stent structure of the present invention of any of the embodimentsdescribed above with helical portions interposed between strut portions.In one embodiment, biocompatible graft material 62 covers outside 64 ofstent graft 60, as shown in FIG. 10A. Alternatively, biocompatible graftmaterial 62 covers inside 74 of stent 70, as shown in FIG. 10B.Alternatively, graft material 62 covers outside 64 and inside 74 ofstent 80, as shown in FIG. 10C. Graft material 62 can be formed of anynumber of polymers or other biocompatible materials that have been wovenor formed into a sheet or knitted surface. Alternatively, the stent canbe coated with a polymer and/or drug eluting material as are known inthe art.

FIGS. 11A-11J are side profile views of stent grafts including thefeatures of the flexible stent structure of the present invention.

Stent graft 100 comprises a continuous covering of graft material 102covering stent 10, as shown in FIG. 11A. Graft material 102 is attachedto strut portions 12. Graft material 102 covers and is not attached tohelical portions 14.

Stent graft 110 comprises a plurality of sections 111 of graft material112 covering the stent structure, as shown in FIG. 11B. Graft material112 is attached to strut portions 12. Graft material 112 covers at leasta portion of helical portions 14 and is not attached to helical portions14. Gap 115 is positioned between adjacent sections 111 of graftmaterial 112. Gap 115 will typically range in size between 0 (meaning nogap) and about 20% of the length of helical portion 14.

Stent graft 120 comprises a plurality of sections 121 of graft material122 covering the stent structure, as shown in FIG. 11C. Graft material122 is attached to strut portions 12. Graft material 122 covers and isnot attached to helical portions 14. Sections 121 of graft material 122are positioned such that there is an overlap 125 between adjacentsections 121 of graft material 122. Overlap 125 will typically range insize between 0 (meaning no gap) and about 40% of the length of helicalportion 14.

Stent graft 130 comprises a continuous covering of graft material 132,as shown in FIG. 11D. Graft material 132 is attached to strut portions12. Graft material 132 covers and is not attached to helical portions14. Graft material 132 has bulge 133 at helical portions 14.

Stent graft 140 comprises a continuous covering of graft material 142,as shown in FIG. 11E. Graft material 142 has a plurality of longitudinalopenings 144 over helical portions 14.

Stent graft 150 comprises a continuous covering of graft material 152,as shown in FIG. 11F. Graft material 152 has bulge 153 at helicalportions 14 and has a plurality of longitudinal openings 154 overhelical portions 14.

Stent graft 160 comprises a continuous covering of graft material 162,as shown in FIG. 11F. Graft material 162 has helical openings 164 inhelical portions 14 that correspond to the pitch and angle of helicalportions 14.

Stent graft 170 comprises a plurality of sections 171 of graft material172 covering stent 10, as shown in FIG. 11H. Sections 171 can beattached to strut portions 12 or helical portions 14. Gap 175 ispositioned between adjacent sections 171 of graft material 172. Gap 175will typically range in size between 0 (meaning no gap) and about 20% ofthe length of helical portion 14.

Stent graft 180 comprises a plurality of sections 181 of graft material182 covering stent 10, as shown in FIG. 11J. Sections 181 can beattached to strut portions 12 or helical portions 14. Sections 181 ofgraft material 182 are positioned such that there is an overlap 185between adjacent sections 181 of graft material 182. Overlap 185 willtypically range in size between 0 (meaning no gap) and about 40% of thelength of helical portion 14.

FIGS. 12A, 12B and 12C are plan views of stent 200 in accordance withthe present invention. FIG. 12A shows stent 200 in an expanded statewith gap 202 between helical elements 18. FIGS. 12B and 12C show stent200 in two different compressed states. In FIG. 12B stent 200 iscompressed such that gap 212 between side-by-side helical elements 18 isabout the same throughout helical portion 14. The size of gap 212between side-by-side helical elements 18 can range between 0 and aboutthe size of the gap 202 in the expanded state, for example, as shown inFIG. 12A. In other words, when the size of the gap is 0, there is nospace between side-by-side helical elements 18 and side-by-side helicalelements 18 contact one another.

The helical elements of the stent shown in FIG. 12B have been wrappedaround the stent a number of times such that in the crimped state theoverall length 211 of the stent in the crimped state is the same as theoverall length 201 of the stent in the expanded state shown in FIG. 12A,thereby eliminating foreshortening.

In FIG. 12C stent 200 is compressed such that helical element 18 iselongated and gap 222 between side-by-side helical elements 18 variesthroughout the axial length of helical portion 14. The size of gap 222between adjacent helical elements 18 can range between 0 and about thesize of the gap 202 in the expanded state, for example, as shown in FIG.12A. In other words, when the size of the gap is 0, there is no spacebetween side-by-side helical elements 18 and side-by-side helicalelements 18 contact one another. In FIG. 12C, the overall length 221 ofthe stent in the crimped state is greater then the overall length 201 ofthe stent in the expanded state.

An additional method can be provided to crimp the stent such that thelength of helical portions is shorter in the crimped state than in theexpanded state. For example, if the stent of FIG. 12A were crimpedsimilar to that shown in FIG. 12B, except no gap exists betweenside-by-side helical elements the stent would be have length 211 in thecrimped state which is shorter than length 201 in the expanded state. Inone embodiment, a method of crimping provides a stent where the overalllength is the same in the crimped and expanded state and there is no gapbetween helical elements in the crimped state.

As described above, one preferred embodiment of the stent is to permitrepeated axial compression or expansion of about 20% and simultaneouslypermit bending with a minimum bending radius of about 13 mm. One methodto construct a stent of the present invention with a specific target forflexibility is to vary the ratio between the sum of the gap space in thehelical portion to the overall length. By increasing that ratio, theflexibility of the stent increases. This ratio will also beapproximately the maximum axial compression the stent will allow. Itwill be appreciated that the maximum axial compression for safety may belimited by other factors such as strain in the helical elements.

FIG. 13 is a plan view of a stent 300 in accordance with the presentinvention. Stent 300 is similar to other embodiments described aboveexcept it includes various configurations and various axial lengths ofstrut portions and various configurations and various axial lengths ofhelical portions. Strut portions 302 positioned at the outer mostportion of stent 300 includes long strut elements 301. Long strutelements 301 have length 311. Length 311 of long strut element 301 isgreater than length 312 of strut portions 304 positioned at the innerportion of stent 300. Long strut elements 301 provided on the ends ofthe stent may be advantageous to provide better anchoring and provide anarea for adjacent stents to overlap, but not impede the flexibility ofthe helical portion. In some vasculatures, notably the femoropoplitealarteries, the length of diseased artery may be long, often longer than10 cm. Multiple stents may be required to treat these long sections ofdiseased arteries. A common procedure in this case is to overlap theadjacent stents so that the vessel being treated is covered. When someconventional stents are overlapped in this manner, the mechanism whichmakes them flexible is impeded and this artificial stiffening can causemany problems, including stent fractures. An advantage of the presentinvention is that the elements that allow bending and axial flexibility(helical portion) are different than the elements that provide radialstructure (strut portion) so that the strut portions on adjacent stentsmay overlap and not impede the movement of the helical portion andtherefore the overall flexibility of the stent.

Helical portion 303 that is adjacent to the strut portion 302 compriseshelical elements 18 that are connected to every strut element 301 ofstrut portion 302. Helical portion 303 can provide a high percentage ofsurface area for optimized delivery of a drug or other therapeuticagent. Strut portion 304 is connected to helical portion 303 by helicalelement 18 at every strut element 16 a on side 320 of strut portion 304and is connected to helical portion 309 at every other strut element 16a on side 321 of strut portion 304. Helical portion 309 provides a lowerpercentage of surface area and greater flexibility than helical portion303. This type of configuration can provide a transition from a stifferhelical portion that has a high percentage of surface area to a moreflexible helical portion.

Helical portion 309 has a higher ratio of the sum of gap lengths 323 tolength 324 of helical portion 309 than the sum of gap lengths 325 tolength 326 of helical portion 303, so that helical portion 309 willgenerally have greater flexibility.

Strut portion 306 has half as many strut elements 305 as strut portions302 or 304 and therefore generally has more open area compared to strutportion 302 or strut portion 304. An advantage of a stent including aportion having a larger open area than other portions of the stent isthat the larger open portion of the stent can be placed over an arterialbifurcation and not impede blood flow. Whereas the strut portion with ahigher strut element density may impede blood flow.

The stent structure of the present invention, namely flexible helicalportions flanked on either side by strut portions, provide an optimizedstructure where the strut portions stabilize a naturally unstablehelical structure, and the helical portions provide net flexibility.There is substantial design optimization potential in combining variousembodiments of the two portions.

The flexible stents and stent grafts of the present invention may beplaced within vessels using procedures well known in the art. Theflexible stents and stent grafts may be loaded into the proximal end ofa catheter and advanced through the catheter and released at the desiredsite. Alternatively, the flexible stents and stent grafts may be carriedabout the distal end of the catheter in a compressed state and releasedat the desired site. The flexible stents or stent grafts may either beself-expanding or expanded by means such as an inflatable balloonsegment of the catheter. After the stent(s) or stent graft(s) have beendeposited at the desired intralumenal site, the catheter is withdrawn.

The flexible stents and stent grafts of the present invention may beplaced within body lumen such as vascular vessels or ducts of any mammalspecies including humans, without damaging the lumenal wall. Forexample, the flexible stent can be placed within a lesion or an aneurysmfor treating the aneurysm. In one embodiment, the flexible stent isplaced in a super femoral artery upon insertion into the vessel, theflexible stent or stent grafts provides coverage of at least about 50%of the vessel.

Although presently preferred embodiments of the present invention havebeen disclosed for illustrative purposes, those skilled in the art willappreciate that many additions, modifications, and substitutions arepossible without departing from the scope and spirit of the invention asdefined by the accompanying claims. For example, a stent could be madewith only right-handed or only left-handed helical portions, or thehelical portions could have multiple reversals in winding directionrather than just one. Also, the helical portions could have any numberof turns per unit length or a variable pitch, and the strut rings and/orhelical portions could be of unequal length along the stent.

1. Flexible stent comprising: a helical portion comprising a pluralityof side-by-side, individual helical elements helically wound about anaxis of said stent, said helical portion being expandable radially upondeployment and compressible, expandable and bendable in a deployedstate; and a strut portion on either side of said helical portion, eachof said strut portions comprising axially aligned strut elements havinga first end connected to said helical elements of said helical portion,said strut portions being radially expandable upon deployment.
 2. Thestent of claim 1 wherein said helical elements are wound at least 90degrees between said strut elements connected to said helical elementsin said deployed state.
 3. The stent of claim 1 wherein said helicalelements are wound at least 360 degrees between said strut elementsconnected to said helical elements in said deployed state.
 4. The stentof claim 1 further comprising one or more additional said helicalportions and one or more additional said strut portions wherein one ofsaid one or more additional said helical portions is connected to asecond end of one of said strut portions, said one or more additionalsaid helical portions being connected respectively to said one or moreadditional said strut portions such that each of said helical portionsis interposed between a pair of said strut portions.
 5. The stent ofclaim 4 wherein said helical elements of each of said helical portionsare wound in the same direction.
 6. The stent of claim 4 wherein saidhelical elements of at least one of said helical portions are wound in adirection opposite to said helical elements of another of said helicalportions.
 7. The stent of claim 1 wherein one or more pairs of helicalportions are separated and flanked by said strut portions, said helicalelements of one portion of said pair being wound in a direction oppositeto said helical elements of the other portion of said pair.
 8. The stentof claim 1 wherein said strut elements of said strut portion have a wavepattern of individual wave portions, each individual wave portion havinga peak.
 9. The stent of claim 8 wherein each of said helical elements isconnected to a respective one of said peaks of said strut elements. 10.The stent of claim 8 wherein some of said helical elements are connectedto some of said peaks of said strut elements.
 11. The stent of claim 8wherein every other one of said peaks of said strut elements areconnected by a respective one of said helical elements.
 12. The stent ofclaim 8 wherein said strut portion comprises a plurality of said strutelements and peaks of said individual wave members being connected toone another by a link.
 13. The stent of claim 4 wherein at least one ofsaid strut portions comprises a plurality of said strut elements, saidstrut elements of said strut portion have a wave pattern of individualwave portions, each individual wave portion having a peak and peaks ofsaid individual wave members being connected to one another by a link.14. The stent of claim 13 wherein said at least of said one strutportions is at either end of said stent.
 15. The stent of claim 1wherein said helical elements extend helically in a first direction froma first said strut element to a peak and then in an opposite directionfrom said peak to a second said strut element.
 16. The stent of claim 1further comprising one or more additional said helical portions and oneor more additional said strut portions wherein one of said one or moreadditional said helical portions is connected to a second end of one ofsaid strut portions, said one or more additional said helical portionsbeing connected respectively to said one or more additional said strutportions such that each of said helical portions is interposed between apair of said strut portions and at least one of said helical portionscomprise helical elements which extend helically in a first directionfrom a first said strut portion to a peak and then in an oppositedirection from said peak to a second said strut portion.
 17. The stentof claim 16 wherein at least one of said helical portions comprises saidhelical elements being wound in a direction opposite to said helicalelements of another of said helical portions.
 18. The stent of claim 1wherein said helical portion has a larger diameter than said strutportions.
 19. The stent of claim 4 wherein at least one of said helicalportions has a larger diameter than at least one of said strut portions.20. The stent of claim 1 wherein said helical portion has a smallerdiameter than said strut portion.
 21. The stent of claim 4 wherein atleast one of said helical portions has a smaller diameter than at leastone of said strut portions.
 22. The stent of claim 1 further comprisinga biocompatible graft material covering an outside surface of saidstent.
 23. The stent of claim 1 further comprising a biocompatible graftmaterial covering an inside surface of said stent.
 24. The stent ofclaim 1 further comprising a biocompatible graft material covering andan outside surface and an inside surface of said stent.
 25. The stent ofclaim 1 further comprising a biocompatible graft material attached to atleast one of said strut portions, said graft material covering saidstrut portions and said helical portion.
 26. The stent of claim 1further comprising a plurality of sections of biocompatible graftmaterial, each of said sections of graft material being attached to oneof said strut portions and covering the attached said strut portion anda portion of an adjacent said helical portion wherein a gap is providedbetween each of said sections of graft material.
 27. The stent of claim26 wherein said gap is less than about 20% of a length of said helicalportion.
 28. The stent of claim 1 further comprising a plurality ofsections of a biocompatible graft material, each of said sections ofgraft material being attached to one of said strut portions and coveringthe attached said strut portion and an adjacent said helical portionwherein said graft material of adjacent sections of graft material isoverlapped.
 29. The stent of claim 28 wherein said overlap is less thanabout 40% of a length of said helical portion.
 30. The stent of claim 1further comprising a biocompatible graft material, said graft materialbeing attached to at least one of said strut portions, said graftmaterial covering said strut portions and said helical portion and saidgraft material having a bulge at said helical portion.
 31. The stent ofclaim 1 further comprising a biocompatible graft material, said graftmaterial being attached to at least one of said strut portions, saidgraft material covering said strut portions and said helical portion andsaid graft material having a plurality longitudinal openings in saidgraft material over said helical portion.
 32. The stent of claim 1further comprising a biocompatible graft material, said graft materialbeing attached to at least one of said strut portions and covering saidstrut portions and said helical portion, said graft material having abulge at said helical portion and said graft material having a pluralityof longitudinal openings in said graft material over said helicalportion.
 33. The stent of claim 32 further comprising a biocompatiblegraft material, said graft material being attached to at least one ofsaid strut portions and covering said strut portions and said helicalportion, said graft material having a plurality of helical openingscorresponding to a pitch of said helical elements.
 34. The stent ofclaim 1 further comprising a plurality of sections of biocompatiblegraft material each of said sections being attached to either said strutportion or said helical portion.
 35. The stent of claim 34 wherein a gapis provided between each of said sections of said graft material. 36.The stent of claim 35 wherein said gap is less than about 20% of alength of said helical portion.
 37. The stent of claim 1 furthercomprising a plurality of sections of biocompatible graft material eachof said sections being attached to either said strut portion or saidhelical portion wherein adjacent sections of graft material areoverlapped.
 38. The stent of claim 37 wherein said overlap is less thanabout 40% of a length of said helical portion.
 39. The stent of claim 1wherein a gap between adjacent helical elements of a helical portion isabout the same in a compressed state of said stent.
 40. The stent ofclaim 39 wherein said gap is in a range of between 0 and a size of a gapbetween adjacent helical elements of a helical portion in said deployedstate.
 41. The stent of claim 1 wherein adjacent helical elements of ahelical portion contact one another in a compressed state.
 42. The stentof claim 1 wherein a gap between adjacent helical elements of a helicalportion varies along the length of said helical portion in a compressedstate.
 43. The stent of claim 42 wherein said gap is in a range ofbetween 0 and a size of a gap between adjacent helical elements of ahelical portion in said deployed state.
 44. The stent of claim 4 whereinsaid strut portions and/or said helical portions can have a varied axiallength over a length of said stent.
 45. The stent of claim 44 whereinsaid strut elements of said strut portion have a wave pattern ofindividual wave portions, each individual wave portion having a peak andeach of said helical elements is connected to a respective one of saidpeaks on one side of said side strut elements and some of said helicalelements are connected to some of said peaks on the other side of saidside strut elements.
 46. The stent of claim 45 wherein every other oneof said peaks of said strut elements are connected by a respective oneof said helical elements.
 47. The stent of claim 4 wherein one of saidhelical portions has a higher ratio of a sum of gap lengths to a lengthof the helical portion than a second one of said helical portions. 48.The stent of claim 4 wherein one of said strut portions has less strutelements than a second of said strut portions.
 49. The stent of claim 48wherein said one of said strut portions has half as many strut elementsas the second of said strut portions.
 50. Flexible stent comprising: ahelical portion comprising a plurality of side-by-side, individualhelical elements helically wound about an axis of said stent, saidhelical portion being expandable radially upon deployment andcompressible, expandable and bendable in a deployed state; and a strutportion on either side of said helical portion, each of said strutportions comprising helically aligned strut elements having a first endconnected to said helical elements of said helical portion, said strutportions being radially expandable upon deployment.
 51. The stent ofclaim 50 wherein each of said helical elements extends for one or morecomplete rotations of 360 degrees about an axis of said stent.
 52. Thestent of claim 50 wherein each of said helical elements extends for atleast 90 degrees about an axis of said stent.
 53. A method forminimizing or eliminating foreshortening of a flexible stent comprisingrotating a plurality of side-by-side individual helical elements, saidhelical elements being helically wound about an axis of said stent toform a helical portion, said helical portion being expandable radiallyupon deployment and compressible, expandable and bendable in a deployedstate and a strut portion on either side of said helical portion, eachof said strut portions comprising axially aligned strut elements havinga first end connected to said helical elements of said helical portion,said strut portions being radially expandable upon deployment.
 54. Themethod of claim 53 wherein an axial length of said stent in saiddeployed state is the same as an axial length of said stent in a crimpedstate.
 55. The stent of claim 53 wherein a gap between said side-by-sidehelical elements of said helical portion is about the same in a crimpedstate of said stent.
 56. The stent of claim 53 wherein said side-by-sidehelical elements of said helical portion contact one another in acrimped state of said stent.
 57. The method of claim 56 wherein an axiallength of said stent in said deployed state is the same as an axiallength of said stent in a crimped state.
 58. The method of claim 53wherein an axial length of said stent in a crimped state is less than anaxial length of said stent in said deployed state.
 59. A method forcrimping a flexible stent comprising elongating a plurality ofside-by-side individual helical elements to a crimped state, saidhelical elements being helically wound about an axis of said stent toform a helical portion, said helical portion being expandable radiallyupon deployment and compressible, expandable and bendable in a deployedstate and a strut portion on either side of said helical portion, eachof said strut portions comprising axially aligned strut elements havinga first end connected to said helical elements of said helical portion,said strut portions being radially expandable upon deployment.
 60. Thestent of claim 59 wherein a gap between said side-by-side helicalelements of said helical portion varies along a length of said helicalportion in said crimped state.
 61. The method of claim 59 wherein anaxial length of said stent in said deployed state is less than an axiallength of said stent in said crimped state.
 62. A method for placing aflexible stent within a mammal in a body lumen comprising placing one ormore stents at said site, said flexible stent comprising a helicalportion comprising a plurality of side-by-side, individual helicalelements helically wound about an axis of said stent, said helicalportion being expandable radially upon deployment and compressible,expandable and bendable in a deployed state; and a strut portion oneither side of said helical portion, each of said strut portionscomprising axially aligned strut elements having a first end connectedto said helical elements of said helical section, said strut portionsbeing radially expandable upon deployment.
 63. The method of claim 62wherein the mammal is a human and the body lumen is a vessel or duct.64. The method of claim 62 wherein the mammal is a human and the bodylumen is a super femoral artery.
 65. The method of claim 62 wherein saidstent further comprises a biocompatible graft material covering anoutside surface of said stent and/or an inside surface of said stent.66. A method of treating a diseased vessel or duct comprising the stepsof: guiding a catheter to a target site; advancing through the cathetera flexible stent, said flexible stent comprising a helical portioncomprising a plurality of side-by-side, individual helical elementshelically wound about an axis of said stent, and a strut portion oneither side of said helical portion, each of said strut portionscomprising axially aligned strut elements having a first end connectedto said helical elements of said helical section; expelling the stentfrom the catheter at the target site, causing the helical portion toexpand radially and said strut portions to expand radially, said helicalportion being compressible, expandable and bendable in a deployed state.67. The method of claim 66 wherein said target site is a vascular site.68. The method of claim 66 wherein the target site is a super femoralartery.
 69. The method of claim 66 wherein said target site is a lesion.70. The method of claim 66 wherein said target site is an aneurysm. 71.The method of claim 66 wherein said stent further comprises abiocompatible graft material covering an outside surface of said stentand/or an inside surface of said stent.
 72. The method of claim 66wherein said stent further comprises a coating of a polymer and/or drugeluting material.